Moreover, we found that:

• The response of heterotrophic nanoflagellates to salinity and temperature differs between taxa and this difference is more pronounced for temperature. The taxon-specific responses result in a shift in community composition. The turnover of differently adapted cryptic species with similar feeding preferences and predator-prey interactions may stabilise microbial food webs facing environmental change.
• The effects of multiple stressors on litter decomposition in freshwater ecosystems showed an overall antagonistic effect
• Globally, effects of flow modification consistently moderated the effects of other stressors on bacterial communities. Taking advantage of ExStream experiments that are set up in multiple countries, we were able to retrieve samples for metagenomics from streams in New Zealand, Ireland, and Brazil. We tested the effects of different stressors applied to these systems depending on the setup with reduced flow velocity being the consistent stressor shared among all of them.

Our studies on multiple stressor effects lay support to several of our initial Main Hypotheses. In particular, Main Hypothesis MH1 on the differential effects of water quality and hydromorphological stressors, and MH3 that biotic interactions modify the organisms’ response to stressors.